1. Field of the Invention
The present invention relates to a catalyst comprising a thin annular shell of catalytically active material deposited on and bonded to an inert, non catalytically active core. The catalyst can be made by depositing a thin coating of finely divided catalytically active material suspended in a colloidal dispersion of boehmite/pseudo boehmite in solvent on a particle of inert material having surface active sites e.g., alpha alumina, and calcining to convert the boehmite into gamma alumina containing the finely divided catalytically active material suspended in it, thereby bonding the annular layer and its contents to the inert e.g., alpha alumina core. Alternatively, a thin layer of colloidal boehmite/pseudo boehmite alone can be deposited on the core and calcined to convert it into gamma alumina which is subsequently loaded with catalytically active metal and, if desired, activity enhancers such as phosphorous, halogen and boron, and mixtures thereof.
2. Description of the Related Art
Platinum on fluorided alumina are known to be effective catalysts for the isomerization of waxes and for upgrading distillates and raffinates. The most selective catalysts for the conversion of wax into isomerate oil contains fluoride in the range 0.1 to less than 2 wt.% and employs small size particles of less than 1/16 inch diameter.
There is an incentive, therefore, to make low fluoride catalyst in particles smaller than 1/16 inch diameter but resort to particles of much less than 1/20 inch, such as 1/20 inch trilobes, could result in weaker particles which easily crumble or fracture and thereby contribute to pressure drop and plugging problems in the reactor. Despite these concerns, however, smaller catalytically active particles are desirable as a way of controlling and minimizing the diffusion effect attributable to larger particles.